A radiation therapy device, in which an irradiation device (radiation source) is supported in such a way as to be able to rotate around a diseased site, is known. The rotation of the irradiation device allows the irradiation device to irradiate the diseased site with radiation beams from various directions. Accordingly, it is possible to reduce an irradiation dose to each of the surrounding normal tissues while securing an irradiation dose required to treat the diseased site.
A radiation therapy device, in which the rotation axis of an irradiation device can be rotated, is known. For example, in a radiation therapy device disclosed in PTL 1, an O-shaped ring supports a traveling gantry, and the traveling gantry supports a therapeutic irradiation device via a swing mechanism. The rotation of the O-shaped ring and the traveling gantry allows the therapeutic irradiation device to move in three dimensions. Accordingly, the therapeutic irradiation device is capable of irradiating a diseased site with radiation beams from various directions, and more reliably reducing an irradiation dose to a vulnerable site.